Aqueous bleach bath

ABSTRACT

AQUEOUS ACIDIC BLEACH BATH BASED ON HYDROGEN PEROXIDE AND ORGANIC CYANIDES.

3,756,774 Patented Sept. 4, 1973 hce 3,756,774 AQUEOUS BLEACH BATH UweKirner, Bobenheim-Roxheim, Germany, assignor to Badische Anilin- &Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany NoDrawing. Filed Sept. 20, 1971, Ser. No. 182,158 Claims priority,application Germany, Sept. 25, 1970, P 20 47 289.3 Int. Cl. D06l 3/02US. Cl. 8111 6 Claims ABSTRACT OF THE DISCLOSURE Aqueous acidic bleachbath based on hydrogen peroxide and organic cyanides.

This invention relates to an aqueous bleach bath based on hydrogenperoxide with which bleaching may be carried out in an acid medium,particularly bleaching of cellulosic textile materials.

The bleaching of cellulosic fibrous materials has hitherto been carriedout with aqueous alkaline hydrogen peroxide solutions because alkalinehydrogen peroxide is notable for a particularly strong oxidizing action.Moreover, the fabric is hydrophilic and shows excellent whiteness aftera single bleaching step.

In order to prevent unduly rapid decomposition of the hydrogen peroxide,sodium silicate or sodium-pyrophosphate is added to such bleach baths.These chemicals form undesirable deposits on parts of the machines, onthe padding equipment or on the textile material being treated,particularly in continuous operation.

Another disadvantage is that all types of cellulose may not beadvantageously bleached under alkaline conditions, as alkalis frequentlyeffect a change in the structure of cellulose.

Attempts have therefore been made to carry out bleaching under acidconditions, mainly in order to stabilize the hydrogen peroxide by meansof acids so that the addition of silicates or similar substances wouldno longer be necessary. The main difiiculty in this case, however,resides in the fact that, under acid conditions, the rate ofdecomposition of the hydrogen peroxide is so low that the bleachingelfect produced by a simple hydrogen peroxide bleach does not come up tothe desired standard. Moreover, the cellulose fibers are chemicallyattacked by the acid, particularly at elevated temperatures, giving riseto the risk of an excessive fall in the average degree of polymerizationafter such a bleaching operation.

Greater success has been achieved in the field of acid bleaching at pHsof about 5 to 6 not with hydrogen peroxide itself but with one of itsorganic derivatives, peracetic acid, produced in the bleach bath by theaddition of acetic anhydride and hydrogen peroxide. This method wascarried out for a period on a commercial scale but was found to be toodangerous, since the second peroxidic compound produced as a co-productof the aforementioned reaction, diacetyl peroxide, was often the causeof violent explosions. At relatively high concentrations, diacetylperoxide can, on account of its relatively poor solubility in water,separate out in the solid form and then decompose explosively.

For this reason, attention was soon redirected to possibilities ofbleaching under alkaline conditions (at pHs greater than 9), attemptsbeing made to replace the silicate by other stabilizers or activators,as taught, for example, in US. Pat. 3,350,161. In that specification,use is made of an adduct of hydrogen peroxide and urea. Thisperoxide/urea adduct decomposes in aqueous solution to form urea andhydrogen peroxide. This process may be carried out at pHs between 9 and13. Its drawback is that it is frequently necessary to improve thebleaching action by adding further bleaching agents such as sodiumchloride or buffers and/or other organic stabilizers. In other words,the unduly rapid consumption of the peroxide must be compensated for bythe addition of further bleaching agents.

German published application DAS 1,018,181 also teaches a bleachingmethod which, according to the examples, may be carried out underalkaline conditions (pH=about 9). In this case, the problem has beentackled with the use of nitriles and it is stated in said applicationthat the addition of nitriles greatly accelerates the liberation ofoxygen. However, to obtain better results using this method, it is stillnecessary to add stabilizers such as sodium silicate, which isunderstandable from the fact that nitriles accelerate the liberation ofoxygen from hydrogen peroxide.

Thus there is still an unfulfilled industrial need for a method ofbleaching under acid conditions. It is an object of the invention toprovide an aqueous bleach bath with which the fabric is adequatelybleached and the fibers are not substantially damaged.

It is another object of the invention to enable bleaching of textilematerials and in particular of cellulosic textile materials such ascotton or cotton blended with synthetic fibers to be carried out withthe use of nitriles and hydrogen peroxide.

It is yet another object of the invention to provide a method ofbleaching cellulosic textile materials without parts of the equipmentbeing coated with deposits of additives such as silicates or otherinorganic precipitates.

These and other objects and advantages of the invention are achieved bybleach baths based on hydrogen peroxide and organic cyanides andcontaining from 0.1 to 2.0% by weight of 100% hydrogen peroxide and from0.05 to 1.2% by weight of an organic cyanide, based on the weight of thebath, and which have hydrogen ion concentrations corresponding to pH 4to pH 7.

Suitable cyanides for the bleach baths of the invention are anycompounds or mixtures of compounds containing at least one cyano group.We prefer to use cyanides which are soluble in water or readilydispersible therein. Examples are cyanides of from 3 to 6 carbon atoms,particularly aliphatic cyanides of from 3 to 6 carbon atoms, these notonly being particularly suitable for the bleach bathof the invention butalso being readily available. The cyanides, which are also referred tobelow as nitriles, may, for example, be aliphatic, aromatic orcycloaliphatic and they may contain hetero atoms.

It is convenient to use nitriles which boil above C. and which show noor only very little tendency to distil with steam. Specific examples arephthalonitrile, malonamidonitrile, propionitrile, butyronitrile,malononitrile, succinonitrile, adiponitrile, cyanamide, dicyanodiamideor mixtures thereof.

The hydrogen peroxide may be used in any of the commercially availableconcentrations. Successful results have been obtained by adding hydrogenperoxide to the bleach bath of the invention such that the concentrationof hydrogen peroxide in the bath is from 0.1 to 2.0% by weight andpreferably from 0.2 to 1.0% by weight, equivalent to a concentration-ofactive oxygen in the bath of from 0.5 to 10.0 g./l. and preferably from1 to 5 g./l.

The organic cyanides are added in concentrations of from 0.05 to 1.2%and preferably from 0.1 to 0.7% based on the weight of the bath, theratio of hydrogen peroxide to cyanide groups then being in the range1:0.1 to 1:1 and preferably the range 1:0.15 to 1:05, without theactivity of the bleach bath being substantially reduced.

The bath containing the hydrogen peroxide and organic cyanide must havea hydrogen ion concentration equivalent to a pH of from 4 to 7 andpreferably from 5 to 6.5. This hydrogen ion concentration is obtained byusing the substances commonly employed for pH adjustments or by usingbulfer mixtures, which also prevent a fall in pH during bleaching.Specific examples of such substances are alkali metal and ammoniumcarbonates, bicarbonates, carbamates, and hexamethylene tetramine,primary, secondary and tertiary alkali metal phosphates, polyphosphatesand/or mixtures of said substances. We prefer to use mixtures of primaryand tertiary phosphates, of primary phosphates and bicarbonates or ofbicarbonates and polyphosphates, the proportions being such that theresulting bleach baths have the specified pH.

Alkali metal formates or acetates, urea or formamide may be added to thebaths and, other components commonly used in such baths may also beadded, for example optical brighteners or surface active agents ormixtures thereof, particular examples being anionic and non-ionicwetting agents and detergents.

The bleach bath is generally prepared at room temperature or slightlyelevated temperatures of up to about 40 C. It is possible to use higheror lower temperatures but this usually has no added advantage.

The effect of the bleach baths of the invention is surprising, as itcould not be foreseen that such acidic baths would increase the activityof hydrogen peroxide whilst causing substantially no harm to the fiberswithout any need for the addition of stabilizers. In the pH range 4 to 7the organic cyanide apparently has a double function. At pHs below 7.5the reaction of hydrogen peroxide with the cyanide forms a peroxycarboximide according to the equation:

R-CEH E 0, R-l'J-OOH but on the other hand the organic cyanide does notact as an accelerator in the liberation of oxygen from the hydrogenperoxide (as is the case under alkaline conditions according to theteaching of German published application DAS 1,018,181 for example), asotherwise the fabric would be attacked to a much greater extent in acidmedium.

At a pH of between 4 and 7 the peroxy carboximide appears to berelatively stable and to have a similar property to that exhibited byhydrogen peroxide systems stabilized by sodium silicate under alkalineconditions.

To effect bleaching, the bath prepared in the manner indicated above maybe heated to from 70 to 100 C., and the fibrous material to be bleachedmay be immersed in the bath before or after the desired temperature hasbeen reached. Alternatively, the fibrous material may be impregnatedwith the bleaching liquor and then heated to the bleaching temperaturein known manner, for example by steaming. By high pressure steamingtemperatures of for example up to 130 C. are obtainable. The liquorratio may be from 1:1 to 50:1 depending on the bleaching process used.The treating time should be sufficient to effect bleaching. Bleaching iscomplete under the specified conditions over periods ranging from a fewminutes, for example 1 to 5 minutes (high-pressure steaming) to 3 hours(pad-roll or J-box bleaching). Yet another alternative is to impregnatethe fibrous material and heat it for a few seconds, for Example 5 to 15seconds, at from about 100 to 130 C. and then leave it for a number ofhours, for example up to 24 hours, in the cold impregnated state, bywhich method the cellulosic material often achieves even higher DPvalues.

The advantages of the present method are obvious. It it now possible tobleach in a pH range in which cellulose fibers have hitherto beenstrongly attacked when bleaching with hydrogen peroxide. A particularadvantage is that baths may be prepared which give rise to very cleanworking, since no inorganic deposits are found in the machines or on thesqueezing rolls, and a degree of whiteness is obtained such as hashitherto only been possible when working under alkaline conditions andusing silicates as stabilizers.

In the following examples the parts and percentages are by weight.

EXAMPLE 1 Desized and dried unbleached cotton cloth is impregnated witha solution of the composition:

0.5% of 100% hydrogen peroxide,

0.4% of adiponitrile,

0.2% of sodium tripolyphosphate,

0.02% of adipic acid and 0.4% of an adduct of 10 moles of ethylene oxideand 1 mole of nonyl phenol.

The pH of the liquor is 6.5.

The material treated with this solution is padded to a wet pickup of100% and steamed for 3 hours at from to C. The material is then rinsedwith warm water and then with cold water.

The bleached material is completely free from husks and has a whitenessof from 82 to 85% reflectance (as measured with an Elrephofotometerusing filter R 46 T) depending on the quality of cotton used. Ofparticular note is the fact that the treated material is extremelyhydrophilic.

Similar results are obtained when impregnation liquors of the followingcompositions are used:

0.5% of hydrogen peroxide,

0.6% of benzonitrile,

0.2% of sodium tripolyphosphate and 0.4% of the adduct of 10 moles ofethylene oxide and 1 1 mole of nonyl phenol.

pH adjusted to 7.0 with adipic acid.

0.5 of 100% hydrogen peroxide, 0.2% of adiponitrile,

0.4% of urea,

0.2% of primary sodium phosphate and 0.2% of sodium bicarbonate.

0.5 of 100% hydrogen peroxide, 0.2% of dicyanodiamide, 0.6% of urea,0.2% of primary sodium phosphate and 0.2% of sodium bicarbonate. pH=6.5.

of 100% hydrogen peroxide,

of adiponitrile,

0.6% of sodium formate,

0.2% of sodium tripolyphosphate and 0.4% of the adduct 0f 10 moles ofethylene oxide and 1 mole of nonyl phenol.

EXAMPLE 2 Dry tubular knitted fabric of pure cotton is impregnated witha solution of the following composition:

The material treated with this solution is padded to a wet pickup of100% and steamed at 100 C. for 45 minutes in a perforated conveyorsteamer. Using this method, there is obtained a whiteness having areflectance of 87 to 90% (Elrepho, filter R 46 T) depending on thequality of the cotton used.

EXAMPLE 3 Cotton terry cloth is treated on a winch vat (liquor ratio20:1) with a bleach bath of the following composition:

0.15% of 100% hydrogen peroxide, 0.1% of succinonitrile,

0.08% of primary sodium phosphate, 0.02% of calcined soda and 0.3% ofurea.

After 2 hours at from 90 to 95 C. a whiteness of from 86 to 88%reflectance (Elrepho, filter R 46 T) is obtained. The material has asoft handle and is extremely hydrophilic.

I claim:

1. A process for bleaching cellulosic textile material which comprisestreating said material in an aqueous acidic bleach bath at a liquidratio of from 1:1 to 50:1 and at a temperature of from 70 to 130 C. fora period sufficiently long to effect bleaching of said material, saidbleach bath consisting essentially of water from 0.1 to 2% by Weight of100% hydrogen peroxide and from 0.05 to 1.2% by Weight of an organiccyanide selected from the class consisting of cyanamide, dicyanodiamide,ben zonitrile, phthalonitrile and aliphatic nitriles of 3 to 6 carbonatoms, all percentages being based on the weight of the bath, and saidbath having a hydrogen ion concentration equivalent to a pH of between 4and 7.

2. A process as claimed in claim 1 wherein the hydrogen ionconcentration is equivalent to a pH of from 5 to 6.5.

3. A process as claimed in claim 1 wherein the organic cyanide is acompound selected from the group consisting of phthalonitrile,malonamidonitrile, propionitrile, butyronitrile, malononitrile,succinonitrile, adiponitrile, cyanarni de, dicyanodiamide and mixturesthereof.

4. A process as claimed in claim 1 wherein the organic cyanide is acompound selected from the group consisting of dicyanodiamide, cyanamideand mixtures thereof.

5. A process as claimed in claim 1 wherein said bath additionallycontains urea, formamide or sodium acetate.

6. A process as claimed in claim 1 wherein said bath also contained anadditive selected from the group consisting of alkali metal and ammoniumcarbonates, bicarbonates, carbamates, hexamethylene tetramide, primary,secondary and tertiary alkali metal phosphates, polyphosphates andmixtures thereof for adjustment of the pH.

References Cited UNITED STATES PATENTS 2,927,840 3/1960 Dithmar et a1.8-111 3,163,606 12/1964 Viveen et a1. 252-99 3,457,023 7/1969 Beloguin81l1 3,345,303 10/1967 Schmid et a1 252-186 MAYER WEINBLATT, PrimaryExaminer U.S. Cl. X.R.

